DC-SIGN binding to surface IgM⁺ primary FL cells. Representative FACS plots of 3 FL samples simultaneously stained within the same tube to detect sIgM expression and soluble DC-SIGN binding (n = 6). Analysis (FlowJo) of singlet live cells initially allowed examination of sIgM expression (A). Populations positive for sIgM were gated to determine DC-SIGN binding on these cells. (B) Representative FACS plot of a control experiment to show that recombinant DC-SIGN-Fc binding is not affected by AT10 (anti-CD32) antibody or by the FcR-blocking reagent. (C) Analysis of GeoMFI data (GraphPad Prism) found that expression of sIgM was significantly correlated to binding of DC-SIGN (Spearman rank test). This correlation was confirmed further within samples of FL cells showing double peaks of high and low sIgM expression.